A comparative Study on Photovoltaic and Concentrated
Solar Thermal Power Plants
Mohamed Rashad A. A.El-Samahy Mohamed Daowd Amr M. A. Amin
Academy of Scientific Research
and Technology (ASRT)
Department of Electrical power and machines Engineerin
Faculty of Engineering Helwan University (HU)
Cairo – Egypt Cairo – Egypt
[email protected] [email protected] [email protected] [email protected]
Abstract - Recently solar energy receives a great attention as
an important source of renewable energy. Solar energy is
converted to electrical energy directly through photovoltaic (PV)
or indirectly through concentrated solar power (CSP) system
which converts solar energy to heat energy which in turn can be
used by thermal power station to generate electricity.
This paper present a comparative study between the two types of
solar power (PV&CSP). This study includes types, components,
initial and running costs, efficiency, advantages, disadvantages
and storage systems.
Index Terms - Renewable energy sources; solar photovoltaic;
concentrating solar power; thermal engine; storage systems.
I. INTRODUCTION
The sun is the most plentiful energy source for the earth.
All form of energy like wind, fossil fuel, hydro and biomass
energy have their origins in sunlight. Solar energy falls on the
surface of the earth at a rate of 120 petawatts, this means all
the solar energy received from the sun in one days can
satisfied the whole world’s demand for more than 20 years.
[1].
The potential of several renewable energy source based on
today’s technology is shown in Fig1. Future advances in
technology will lead to higher potential for each energy source.
However, the worldwide demand for energy is expected to
keep increasing at 5 percent each year. Solar energy is the only
choice that can satisfy such a huge and steadily increasing
demand. [2].
Fig. 1: The Potential for Renewable Energy Source
Renewable energy is the energy which comes from natural
resources such as sunlight, wind, rain, tides and geothermal
heat. These resources are renewable and can be naturally
replenished. Therefore, for all practical purposes, these
resources can be considered to be inexhaustible [3].
Among renewable energy source, solar technologies are
capturing large interest. Most of the solar power systems in the
market today can be divided into two major classes: the direct
and the indirect solar power. The direct solar power refers to a
system that converts solar radiation directly to electricity using
a photovoltaic (PV) cell. The indirect solar power refers to a
system that converts the solar energy first to heat and after that
to electrical energy, as in the case of concentrated solar power
(CSP). In a CSP plant, sunlight is focused on a heat exchanger;
this heat is used to drive the turbine. The problems with these
technologies are inefficiency and a very high capital cost. The
typical efficiency of a CSP is about 15%. the highest efficiency
of a silicon cell for example is 20%.On the other hand,
Concentrating Solar Power (CSP) technology is now acquiring
an increasing interest, especially if built with thermal energy
storage, Moreover; economic issues have been treated for CSP
in order to verify which the profits, the breakeven are and so
on. [4].
The aim of this paper is to compare a PV plant with a CSP
plant from technologies of system, types and components of
system, efficiency, initial costs comparison, advantages,
disadvantages, life cost of electricity (LCOE) and storage
systems
II. PV SYSTEMS
Solar photovoltaic, also called solar cells or PV, are
electronic devices that convert sunlight directly into electricity.
The modern form of the solar cell was invented in 1954 at Bell
Telephone Laboratories. Today, PV is one of the fastest-
growing renewable energy technologies and is expected to
play a major role in the future global electricity generation
mix. A PV system consists of a number of PV cells grouped
together to form a PV module, along with auxiliary
components. [5].
A. PV plants
The PV plants can be categorized into two main
typologies according to the installation mode: stand alone and
grid-connected. The first one refers to PV plants which are not
connected to the electrical grid of the local energy utility
company. This typology of PV plants is usually used to feed
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small electrical load (e.g. for street lighting) or when the
electrical grid is too far (e.g. an isolated rural house). Stand-
alone PV plants have a storage battery with stabilizer in order
to guarantee that: a) the battery is not over-charged by the PV
plant; b) the charge of the battery is not less than a prefixed
threshold; c) the electrical loads may be fed directly from the
DC side of the inverter for DC loads or from the AC side for
AC loads. Anyway, stand-alone PV plants are not used for
high power. The second one refers to the PV plants directly
connected to the electrical grid of the local energy utility
company. In this case, there is no storage battery because the
electrical storage is represented just by the electrical grid. In
fact, the energy produced by the PV plants and not
simultaneously absorbed by the electrical loads is injected in
the electrical grid. Then, when the electrical loads require
more energy than that produced by the PV plant, the lacking
part is taken from the grid. [6]
B. PV Technologies
For describing the use of PV installations is used the
maximum power (Wp) that theoretically the PV module can
provide. The power of solar PV installations is therefore given
in Wp (peak Watts). This power corresponds to the one given
by the solar modules at 25ºC at irradiation conditions of
1000W/m2. There are four ranges of power for PV
installations depending on the location and the number of
housing supplied [7]:
1) Small-sized installations of 3 kWp, up to 5 kWp
2) Medium-sized installations of 30 kWp, with a range
between 5 and 100 kWp t.
3) Big-sized installation of 300 kWp, with ranges
between 100 kWp and 1 MWp..
4) 3MWp photovoltaic plants, with ranges between 1
and 50 MWp.
C. PV Concentrators
Concentrating PV (CPV) systems use refractive lenses or
reflective dishes to concentrate sunlight onto solar cells in
order to make benefit of a higher concentration ratio (CR).
There are many types of concentrators, the most known are
[8]:
1) Compound Parabolic Concentrator (CPC)
2) Paraboloid Reflector.
3) V-Trough Concentrators
4) Fresnel’s Lenses
Four important parameters are taken into consideration in
order to make the comparison between most important PV
concentrators; these parameters are:
Construction.
Concentration ratio.
Reflection.
Tracking system
The comparison of the studied photovoltaic concentrators
is given in Table 1. Based on the obtained results in this table,
and depending on any project requirements, the PV
concentrator can be selected.
A. Components of the PV Plant
The complete system of typical photovoltaic plant
includes different components that should be selected taking
into account the individual needs, site location, climate and
expectations. The functional and operational requirements will
determine which components the system will include major
components such as [7]:
1) PV Modules, to convert sunlight instantly into DC
electric power
2) Inverter, to convert DC power into standard AC
power.
3) Battery, to store energy
4) Transformer, to change the voltage in the installation
for being able to connect with the distribution network. It is
used a low voltage – medium voltage transformer.
5) Utility Meter: utility power is automatically provided
at night and during the day when the demand exceeds the solar
electric power production. The utility meter actually spins
backwards when solar power production exceeds house
demand, allowing you to credit any excess electricity against
future utility bills.
6) Charge Controller, to prevent battery overcharging.
Table1. Comparison between different types of PV concentrators. [9]
Types Compound Parabolic Paraboloid Reflector V-Trough Fresnel's Lense
Construction Made by two segments
of parabolas
Use an anodized Al or simply a
glass mirror which has a high
reflectivity
Use arrays of trough shaped
mirror
Made of several prisms
arranged either linearly or in
concentric circles
Concentration
Ratio (CR) 1/sin𝜃𝑎 𝜋𝑟2/𝐴𝑐𝑒𝑙𝑙 sin[(2𝑛+1)𝜓+𝜃]/sin(𝜓+𝜃) 𝐿.𝑊/𝐴𝑐𝑒𝑙𝑙
Reflection of
parallel ray
into
Point Point Line Point or Line
Tracking
system
Not continuous
tracking Two axis Not exist Two axis
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In addition, there are some component of hardware to
complete the system and to make balance of system such as;
wiring, over current, surge protection and disconnect devices,
and other power processing equipment.
B. Life Cost of Electricity (LCOE)
The LCOE varies by technology, country and project
based on the renewable energy resource, capital and operating
costs, efficiency and performance of the technology.
Fig. 2: shows the LCOEs resulting from achieving the
installed PV system prices. These LCOEs are calculated using
assumptions about O&M expenses, inverter efficiencies, and
derate factors (due to losses in wiring, diodes, or shading) [9]
As shown in Fig. 2, assuming the targets are met by 2020,
residential PV is projected to be increasingly competitive with
residential electricity rates, commercial PV is projected to be
increasingly competitive with commercial electricity rates, and
utility-scale PV is projected to be increasingly competitive
with whole sale electricity rates. Utility-scale PV LCOEs
become competitive with California’s Market Price Referent
(MPR), which is used as a benchmark to assess the value of
renewable generation in California (CPUC 2011), by 2015 at
higher costs than those targeted in the scenario. This illustrates
that, while achieving price targets will allow PV to compete
broadly with conventional generation in several U.S. markets
C. Solar PV capital costs
The capital cost of a PV system is composed of the PV module
cost and the Balance of System (BoS) cost. The cost of the PV
module and the interconnected array of PV cells are
determined by raw material costs, cell
processing/manufacturing and module assembly costs. The
BoS cost includes items such as the cost of the structural
system (e.g. structural installation, racks, site preparation and
other attachments), the electrical system costs include the
inverter, transformer, wiring and other electrical installation
costs) and the cost of the battery or other storage system.
Prices for PV modules have fallen by between 30% and 41%
in the year to September 2012 and by between 51% and 64%
for the two years to September 2012, depending on the
technology and source for European buyers. [5]
Prices for PV systems in the United States have dropped by 50
percent or more in recent years, with the sharpest declines for
large-scale projects. [10]
D. Electrical Storage Systems (ESS)
The major categories of ESS used in PV plants are [11].:
Electro-mechanical electrical energy.
Flywheel Energy Storage Systems (FESS).
Electro-chemical energy.
Battery Energy Storage Systems (BESS) there is a
wide variety of battery technologies both in
production and as topics of research.
Lead Acid batteries.
Capacitor and Super-Capacitor Storage Systems
Electro-magnetic Superconductor Magnetic Energy
Storage (SMES).
III. The Concentrating Solar Power Plant
Concentrating solar power (CSP) is a power generation
technology that uses mirrors or lenses to concentrate the sun’s
rays, in most of today’s CSP systems to heat a fluid and
produce steam. The steam drives a turbine and generates
power in the same way as conventional power plants.
Fig. 2: PV LCOEs by Year and Market Segment
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Fig. 3. The Falling Price of Solar PV by U.S. Sector, 2007–2013
A. CSP TECHNOLOGIES
CSP plants can be divided into two groups, based on
whether the solar collectors concentrate the sun rays along a
focal line or on a single focal point. Line-focusing systems
include parabolic trough and linear Fresnel plants and have
single-axis tracking systems. Point-focusing systems include
solar dish systems and solar tower plants and include two-axis
tracking systems to concentrate the power of the sun as shown
in Fig 4. [12]
B. CSP Concentrators Assessment
The aforementioned CSP concentrators’ comparison may
have eight parameters .These parameters are: application, costs,
axis, heat exchange, concentration type, receiver type,
advantage and disadvantage.
The concentrators’ comparative study is given in Table 2;
the best result of the CSP can be deduced.
C. Cost Analysis of CSP
The cost of electricity generation from CSP is
expected to decrease continuously. According to a study
of renewable energy made by the IEA [14], the current
CSP technology systems are implemented in the cost
range of 0.19$/kWh to 0.25$/kWh. In the conventional
power market, CSP competes with mid-load power in
the range of 0.037$/kWh to 0.05$/kWh. As different
scenarios have predicted, the costs of CSP can be
reduced to competitive levels in the next 10 to 15 years.
Competitiveness is affected not only by the cost of the
technology itself, but also by potential price increases of
fossil energy and by the internalization of associated
social costs, such as carbon emissions. Therefore, it is
assumed that in the medium to long term,
competitiveness will be achieved at a level of
0.05$/kWh to 0.075$/kWh for dispatch able mid-load
power.
According to another report prepared by Electric
Power Research Institute, when the global cumulative
capacity of CSP implementation reaches 4GW,the cost
of electricity generation from new plants in 2015 could
be as low as 0.08$/kWh (nominal 2015dollars) or nearly
0.05$/kWh (real 2005 dollars). D. Thermal Energy Storage in CSP Plant
Thermal energy storage (TES) system is an intermediate
and critical subsystem of solar power plant to store and
dispatch the concentrated energy into power block (electricity
generation).
Thermal energy storage technologies are generally
categorized in terms of applied process and loading method
meant to direct thermal storage and indirect thermal storage. In
direct systems, the heat transfer fluid acts as the storage
medium simultaneously, whereas in indirect systems, a storage
medium is different from the transferring fluid, the difference
between them is determined according to the location of the
thermal storage tank related to the medium and transfer
material, heat exchanger (HEX) block, pump, valve and
number of practical utilities. [15]
Fig. 4 Schematics of the Four CSP Approaches for Power Generation. [13]
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ISBN: 978-1-61804-324-5 170
Table2. Comparison between different types of (CSP) [8]
Linear Fresnel Parabolic-Dish Parabolic trough Solar tower Types
Single application
In single application
or grouped in dish
farms
For large grid-
connected power
projects in the 30-200
MW size
For large grid-connected power
projects in the 30-200 MW size Uses
NA
1.3 - 12.6
2.7 - 4.0
2.5 - 4.4
Cost
(USD/W)
Dual Dual Single or dual Dual Axis
Not Need
Not Need
Needed
Needed
Heat
exchange
Focal line
Focal point
Focal line
Focal point
Concentration
on (in case of
parallel rays)
Fixed Mobile Mobile Fixed Receiver
Doesn’t require rotating
coupling between the
receivers and the field
header piping thus
providing additional
design flexibility
Can be placed on a
varied terrain using
small quantities of
water
Concentrating sunlight
to produce ice
With a lower required salt
inventory the operating
temperature is high compared
to in CSP Trough
Advantage
Requires a mirror above
the tube to refocus the
missing rays or a multi-
tube receiver that is large
enough to capture missing
rays without putting a
mirror
The conversion from
heat to electricity
needs the moving of
heavy engine, which
requires a strong
tracking system
A transparent glass
tube envelops the
receiver tube to reduce
heat loss
Each mirror must have its own
dual-axis control
Disadvantage
Primary circuit (oil) Secondary circuit (water)
Fig.5: Conventional CSP Plant with thermal storage and oil as working fluid
Source: IEA (2011), “Solar Energy Perspectives”
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E. CSP Plant Components
Generally, the CSP plants are consisting of three
major components:
Solar field
Thermal conversion
Power generation
Fig. 5 shows the CSP plant components, the concentrating
system and solar receiver, heat transfer and thermal storage,
heat conversion and power generation.
IV. Comparison between (PV) and CSP.
The (PV) and CSP are different in terms of technical
aspects, but both techniques are essential clean energy
alternatives to utilize solar power [14].
PV converts sunlight directly into electricity (DC
power) while CSP converts the light energy into
thermal energy first, then use traditional turbine to
convert heat into electricity (AC power).
PV can use the solar diffuse radiation while CSP
can only convert sun’s direct radiation into power.
Unlike PV’s technique relies mostly on developing
individual cell and module, the CSP technology
relies heavily on the on-site constructing and final
assembling and system integration.
Energy storage of CSP is considerably lower than
that of PV. With storage, power production can be
shifted according to demand therefore is less
dependent on the time period and daily weather
conditions.
The CSP technology is a still undeveloped industry,
which is forced to face the competition and cost
challenge come from the PV system.
The Advantage of CSP over PV and many other
renewable energy technologies is its ability to store
the sun’s energy as heat in molten salts, and to use
it to generate electricity when the sun is no longer
shining and at times when it may be most valuable
to the grid. The molten salt heated by concentrating
the sun’s energy can be stored and kept hot for
several hours. When electricity is needed, the heat
stored in the salts can make the necessary steam.
This storage lets CSP systems extend the “rush
hours” of their generation patterns and generate
electricity a few hours before the sun rises and a
few hours after it sets, making it easier to integrate
electricity from such plants into the grid [10].
Cost comparison between PV versus CSP is
presented in Table 3.
Table 3: Cost Comparison – PV vs. CSP [9]
V. Conclusion
Photovoltaic solar panels (PV) and concentrated
solar power (CSP) are the most two commonly
deployed technologies and are expected to have a
rapid growth in both the short- and long-terms.
Installations of CSP and PV electricity generation
devices are growing rapidly. The PV share of
electricity generation is greatly reduced as CSP is
introduced into the model.
This paper provided a brief summary for those who
are interested in solar energy technologies and as a
reference for those who want to invest or work in this
field. PV and CSP technologies were discussed and
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ISBN: 978-1-61804-324-5 172
reviewed their structure, performance, advantages and
drawbacks. In addition, they have been evaluated and
compared their mechanism, structure, and efficiency, along
with other technical details.
This study shows that PV systems present a noticeable
cost reduction as compared with CSP systems. However, the
effective energy storage offered by CSP systems make than
relevant competitors to PV systems.
Acknowledgement
This work was funded and supported by a grant
from the Academy of Scientific Research and
Technology (ASRT) and the ENPI program of the
European Union through STSMed project. The
authors are grateful to the ASRT and ENPI program.
Additionally, they are appreciative for the reviewers
for their helpful suggestions.
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